The conventional high-voltage power supply generally employs a two-stage converter to convert an input voltage into an output voltage. As shown in FIG. 1, a power supply 100 is configured to convert an AC voltage Vin into an output voltage Vo. The power supply 100 includes a bridge rectifier 120, a power factor correction converter 140, a resonant converter 160, a transformer T100, and an output capacitor C100. The output voltage Vo is used to drive a load Z100. The bridge rectifier 120 is configured to rectify the AC voltage Vin into a full-wave rectified DC voltage. The power factor correction converter 140 is connected to the output end of the bridge rectifier 120 and includes a boost choke Ls, a control switch S100, a diode D100, and a filtering capacitor Cs. The boost choke Ls is used to store the full-wave rectified DC voltage outputted from the bridge rectifier 120 and transfer the stored energy to the filtering capacitor Cs through the diode D100 according to the switching operation of the control switch S100. With the capacitive impedance of the filtering capacitor Cs, the high-frequency harmonics of the input current can be suppressed, thereby improving the power factor of the input voltage Vin. The resonant converter 160 is connected to the output end of the power factor correction converter 140 and includes control switches S102, S104, filtering capacitors C1, C2, a resonant inductor Lr, and resonant capacitors Cs, Cp. The resonant tank formed by the resonant inductor Lr and the resonant capacitors Cs, Cp is used to generate resonance to drive the control switches S102, S104 to switch at the time when the voltage or current of the resonant tank is zero, thereby reducing the switching loss and accomplishing the voltage conversion. Thus, the energy of the AC voltage Vin can be transferred to the secondary side of the transformer. The transformer T100 includes a primary winding Np100 and a secondary winding Ns100, in which the primary winding Np100 is used to store the energy of the AC voltage Vin transmitted from the resonant converter 160 and transfer the stored energy to the secondary winding Ns100 according to the switching operation of the control switches S102, S104, thereby inducing a voltage across the secondary winding Ns100. Therefore, the induced voltage is outputted to the load Z100 through the output capacitor C100, and thus the load Z100 is powered.
The power supply of FIG. 1 is made up of a two-stage converter in which the first stage converter is implemented by a power factor correction converter 140 and the second stage converter is implemented by a resonant converter 160. As a result, the power conversion efficiency of the power supply of FIG. 1 is derived as the product of the power conversion efficiency of the first stage converter and the power conversion efficiency of the second stage converter. Therefore, the power conversion efficiency of the power supply of FIG. 1 is lessened as a result of the multiplication. Also, because the two-stage converter is employed to achieve the power conversion for the power supply, the number of the circuit elements of the power supply is increased, thereby inflating the cost and boosting power loss.